Conclusions and Discussion - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 310

alleles, and F values as affected by inbreeding and/or local genetic
differentiation.
Changing the geometric positioning of the same number of founders
(holding all other factors constant) can result in different trajectories for
rates of change of various population genetics values, these differences
continuing for some time as the population develops.
Introducing founders at densities that approximate the average density
for the species can suppress the growth of newly establishing populations,
even when only a few founders are introduced. This effect can hold not
only within the area of the founders, but also outside that area.
Given the previous fi nding, placing founders at greater distances from
one another than at a species' average density can promote population
growth rates and genetic diversity retention. This also spreads the founders
further, which more quickly increases the area that the species comes to
inhabit, exposes the founders to a wider array of habitat conditions, and
can provide some degree of “bet hedging” against localized factors that can
diminish population growth and genetic diversity (e.g., fi re, pathogens).
Rates of population growth and loss of genetic diversity can be
strongly affected by the degree of density dependence across populations
or species.
Differences in population statistics (growth rates, genetic diversity
change) can be quite large even when apparently minor changes to the
spacing of founders are made between trials.
Most of the population and genetic trend trajectories seen for
NEWGARDEN developing populations (rates of population growth,
loss of heterozygosity, increase in F, loss of unique alleles) are set early
in stand development when population census sizes are low. These
early phases of establishment are thus most important in terms of study,
monitoring, intervention, etc. for improved practices to prevent diversity
loss. NEWGARDEN can be used to model the effectiveness of different
intervention plans.
In several cases studied, different spatial arrangements of the same
number of founders in various trials could lead to differences in population
growth rates but not with regard to genetic diversity retention. However, in
such cases, if r is reduced, resulting in much slower-growing populations,
rates of loss of genetic diversity may then differ among trials.
NEWGARDEN can be used to investigate the effects of varying degrees
of subdivision on population growth and genetic diversity.
Under certain conditions, for expanding populations, subdividing the
founders into isolated smaller groups may increase (1) the rate of population
growth, (2) the rate of loss of heterozygosity, (3) F, and (4) the number of
unique alleles retained as compared to otherwise identical populations
initiated with the same number of relatively non-subdivided founders. Some